PHILADELPHIA – Senate Democrats are confident that their primary races this year will turn out exactly as they hope, with one exception.

Pennsylvania’s Democratic Senate primary is a giant question mark to even seasoned operatives in Washington and the Keystone State. They describe the contest here as a de facto two-person showdown between environmental policy wonk Katie McGinty and Navy veteran and former Rep. Joe Sestak.

The Democratic Party’s power brokers plainly prefer McGinty, and say she’s more personally cooperative than the obstinate Sestak, who has a reputation for going his own way, and ignoring party advice.

McGinty, 52, who was an aide to Vice President Al Gore, has the backing of local labor unions, Emily's List, and former Pennsylvania Gov. Ed Rendell.

Yet her overwhelming institutional support hasn’t helped overcome 64-year-old Sestak’s early lead in the polls , or more surprisingly, his fund-raising advantage. And six weeks before the April 26 primary, that’s led to a sense among Democrats in Pennsylvania that Sestak and not McGinty should be regarded as the race’s narrow front-runner.

A McGinty loss would be a rare hiccup for national Democrats, who expect former Gov. Ted Strickland in Ohio and Rep. Tammy Duckworth in Illinois to cruise to easy victories in their own primaries on Tuesday. In Florida, they’re also confident that a string ofdamaging stories about controversial Rep. Alan Grayson has neutralized the threat he poses to establishment-backed Rep. Patrick Murphy. Like Pennsylvania, all three of those states are currently represented by a Republican senator and are seen as top-tier pickup opportunities by Democrats this fall.

McGinty’s supporters argue that Sestak, the party’s 2010 nominee for Senate, was always going to hold an early advantage because of lingering support from his last campaign and the fact that he became a candidate more than a year earlier. But with the race’s first TV ads airing last week, they also acknowledge that she must make up ground or face mounting criticism that she’s not the right Democrat to face Republican Sen. Patrick J. Toomey in November.

Most professional Democratic operatives consider Sestak personally cool and hostile to outside advice, a feeling symbolized by the candidate’s decision to walk hundreds of miles across the state during the past year – time they feel would have been better spent calling donors and locking down institutional support.

But there’s also a feeling that Sestak, a former admiral who nearly defeated Toomey in 2010 despite that year’s massive Republican wave, could be a better general election candidate than many realize.

Rendell, the ex-governor who is serving as chairman of McGinty’s campaign, says his candidate will have to raise plenty of money fast to prevail in an air war: “There is no campaign in a state our size until there’s TV."

He has already stirred controversy by acknowledging that McGinty has been struggling to raise money and needs a surge of TV ads from outside groups to win.

In an interview with Roll Call , he said he thought raising money for McGinty –- who collected roughly $1 million in contributions in the third and fourth fund-raising quarters -- has been hard because of the Democratic presidential primary and this summer’s Democratic National Convention in Philadelphia.

“I’m helping her as much as I can, but there’s so much competition” for donations from Democrats, said Rendell, the one-time mayor of Philadelphia who estimated that McGinty and allies such as Emily’s List – whose political arm announced an investment on behalf of the candidate last week worth about $1 million -- would need to spend $600,000 a week on TV ads for the next six weeks.

“If they don’t, it’s going to be hard,” he said. “Not impossible, but hard.”

Democratic strategists nationally have always viewed Sestak as this election cycle’s most difficult foe to knock off, and in state, memories are still fresh of the onetime congressman’s 2010 unexpected primary victory over party-switching Democratic Sen. Arlen Specter, who lost despite full-throated endorsements from President Barack Obama, Pennsylvania Sen. Bob Casey, and Rendell.

The bigger worry about McGinty is whether, as a candidate for office, she connects with voters. She has run in just one major race before her current contest, a 2014 gubernatorial campaign in which she finished last in a four-way Democratic primary. Otherwise, her background has been entirely behind-the-electoral-scenes: She’s served as Pennsylvania’s secretary of environmental protection under Rendell, and was most recently chief of staff to Pennsylvania Gov. Tom Wolf, a position she held for six months before resigning to run for the Senate.

One Democratic strategist watching the race compared her to Al Gore, suggesting that although McGinty is impressive in one-on-one settings, she loses something when trying to appeal to broader audiences.

In an interview, she suggested she was similar to Hillary Clinton, who made headlines during a presidential debate last week when she said that she wasn’t a natural politician: “I love people, but I’m more of a work horse than a show horse. I like to roll up my sleeves and get stuff done, and so the kind of talking about it for talking-about-its sake is not my favorite thing to do.”

McGinty doesn’t face only Sestak in April: little-known perennial candidate Joe Vodvarka and Braddock Mayor John Fetterman are also on the ballot. Fetterman, whose hulking stature and unapologetically progressive agenda have helped him attract national attention, is a wildcard, though many Democratic strategists think his relative lack of money make victory a longshot.

Rendell said that though he thinks McGinty would make the stronger candidate, both she and Sestak could defeat the GOP incumbent. (McGinty, notably, declined to say whether she thought Sestak could win over Toomey).

In an interview, Sestak stressed that should he win the nomination, he would cooperate with the Democratic Senatorial Campaign Committee and other party power brokers – but that he would retain his own distinct approach to campaigning.

“I’m kind of toying with the idea of walking 884 miles across the state,” he said, laughing. “And then back.”